Developing a new source of water resources has surfaced as an urgent facing problem due to recent serious pollution of water quality environments and water shortage. Researches on the pollution of water quality environments aim for high-quality residential and industrial water, and treatment of various domestic sewage and industrial wastewater, and interests in water treatment processes using a separation membrane having an advantage of energy saving has been rising. In addition, accelerated reinforcement on environment regulations is expected to advance wide utilization of separation membrane technologies. Traditional water treatment processes are difficult to satisfy the tightened regulations, however, separation membrane technologies secure excellent treatment efficiency and stable treatment, therefore are expected to become a leading technology in the field of water treatment in the future.
Liquid separation is divided into microfiltration, ultrafiltration, nanofiltration, reverse osmosis, stannizing, active transport, electrodialysis, and the like, depending on the pore of the membrane.
Specifically, typical examples of such a water treatment separation membrane include a polyamide-based water treatment separation membrane, and the polyamide-based water treatment separation membrane is manufactured using a method in which a fine porous support is formed by forming a polysulfone layer on nonwoven fabric, and this fine porous support is immersed in an aqueous m-phenylenediamine (mPD) solution to form an mPD layer, and this mPD layer brings in contact with trimesoyl chloride (TMC) by being immersed in a TMC organic solvent or being coated, and is interfacial polymerized to form a polyamide active layer. According to the preparation method described above, a non-polar solvent and a polar solvent are contacted, and polymerization occurs only at the interface, and as a result, a polyamide active layer having a very small thickness is formed.
Meanwhile, there is a qualification for a polyamide-based water treatment separation membrane to be commercially used, and it is having superior capabilities as a separation membrane such as high salt rejection and permeate flow. Salt rejection of a separation membrane commercially required is at least 97% or greater for brackish water, and an ability to have a relatively large amount of water passing through under a relatively low pressure, that is, a high flow property is required.
Meanwhile, together with improving efficiency such as salt rejection and permeate flow of a separation membrane, having high durability against damage and scratches that may occur during manufacturing and modularization processes of a separation membrane, and preventing the contamination of a membrane has recently become an important issue.
In manufacturing and modularization processes of a polyamide-based water treatment separation membrane, the separation membrane needs to go through various processes, and damage and scratches frequently occur on the membrane surface during such processes. A method of forming a polyvinyl alcohol-based coating layer on the surface of a polyamide active layer has been proposed in order to solve such a problem. However, when a polyvinyl alcohol-based coating layer is present on a polyamide active layer, there is a problem in that an active surface area of the polyamide active layer surface decreases due to the coating layer causing significant decrease in permeate flow and salt rejection properties. Accordingly, the coating layer is preferably removed after completing a modularization process in order to improve permeate flow, however, high-temperature water needs to be used to remove the coating layer since polyvinyl alcohol is not favorably dissolved in water at room temperature, and in this case, a problem of damaging the polyamide active layer occurs in the coating membrane removal process.
In addition, in existing polyamide-based water treatment separation membranes, pores of the active layer shrink or moisture content decreases when the polyamide active layer is dried, which causes significant decrease in salt rejection and permeate flow, therefore, separation membranes have always needed to be stored and distributed in a wet state causing inconvenience. This has caused problems in that it lowers economic feasibility of processes, and makes transport and handling difficult.